1. Field of Invention
The present invention relates generally to the field of fluid transfer, and more particularly to pump stages having non-axisymmetric passage contours, pump apparatus and methods of using same.
2. Related Art
Centrifugal pump stages of electrical submergible pumps (ESP) and other centrifugal pumps experience hydraulic losses due to so-called secondary flow patterns that develop within the stage. One example of a secondary flow is the development of vortices near boundaries of flow passages. Common causes of vortices and other secondary flows are Coriolis forces in impellers, and flow passage and blade curvature in impellers and diffusers. The secondary flow is commonly lower velocity than the core or primary flow, and often collects at the suction/hub corner in diffusers and at the pressure/shroud corner in impellers. Secondary flows are undesirable as they result in inefficient pump operation, surging, and in extreme cases, pump failure.
Flow passages in known diffusers are formed by hub and shroud blade contours that are surfaces of revolution about the stage axis. This makes the blade heights on the suction side and on the pressure side equal, or axisymmetric. Axisymmetric contours are the result of presently used stage analysis and design techniques and more importantly, current manufacturing techniques for making the corebox tooling.
There is a need in the fluid transfer art for pump stage designs that reduce the effects of secondary flow.